The invention relates to a process for the preparation of copolymers of carbon monoxide with one or more compounds comprising an ethylenically unsaturated bond.
It is known that copolymers of carbon monoxide and one or more ethylenically unsaturated compounds, in which copolymers the units originating from carbon monoxide substantially alternate with the units originating from the ethylenically unsaturated compounds, may be prepared by reacting the monomers under polymerization conditions in the presence of a suitable catalyst.
These copolymers can be prepared in the liquid phase or in the gas phase. These methods are described in references exemplified by EP 181,014 (liquid phase) and EP 248,483 (gas phase). The gas phase method is preferred for technical and economic reasons. For example, with the gas phase method, isolation and purification of the product is carried out without the need for the additional steps of filtration and centrifugation.
In the known embodiments of the copolymerization process i.e. both in embodiments carried out in the liquid phase and in those carried out in the gasphase, usually a catalyst system is applied which is based on a compound of a metal from Group VIII of the Periodic Table, an anion of a non-halogenic acid with a pKa of less than 2, and a bidentate ligand. It is believed that when using such a catalyst system in a liquid phase operation of the process, polymerization will only occur when an anion originating from the liquid diluent (usually a lower alcohol such as methanol) has been incorporated in the catalyst system. It is further believed that with these catalyst systems, incorporation of a small amount of such anions in the catalyst system is required for obtaining good polymerization results.
It has accordingly been proposed to supply small amounts of a compound generating such anions during the gasphase process, in order to achieve a prolonged polymerization activity of the catalyst system. However, it will simplify the process if the use of such anion generating compounds can be omitted without impairing the polymerization results.
It has now been found that by selecting a particular catalyst system, the presence of the said anion generating compounds can be avoided. Moreover it has been observed that the copolymers thus prepared are characterized by a high degree of crystallinity.